The use of belts and chains to transfer rotary motion in mechanical drive systems is well known. However, despite the maturity of the technology, belts and chains alike suffer from wear and tend to stretch throughout their operational life. To maintain a desired tension in the belts or chains, various known tensioning mechanisms exist today.
In one approach, the position of the sprockets, pulleys of sheaves can be adjusted to change the geometry of the chain or belt's path. Adjustable idler sprockets or pulleys can be included in the path of the chain or belt to adjust the effective length and thus the tension. Idler wheels can be mounted in a spring-loaded manner so as to constantly bias the idler into engagement with the chain or belt with a force dictated by the spring. Such a tensioning mechanism accommodates wear in the chain or belt without adjustment. In practice, one or more of the known tensioning methods may be adopted in the same drive system.
United Kingdom patent application GB-1,228,283 discloses a drive mechanism on a combine harvester having a belt drive for a clean grain elevator. The belt drive includes a lower driving run and an upper driven run. A tensioning mechanism in the form of a pair of idlers mounted on a spring-loaded pivot arm is provided for the upper belt. An intermediate shaft is free to pivot to allow the tensioning of the upper belt to transfer to the lower belt also.
Although not discussed in GB-1,228,283, the tensioning of clean grain elevators is cumbersome in known combine harvesters. Such grain elevators typically include a chain with conveyor elements trained around a pair of sprockets which define the upper and lower limits of the conveyor. One sprocket is driven whilst the other sprocket idles. It is preferred that the sprocket at the discharge end of the conveyor is driven rather than the intake end because the operating tension in the chain under load only impacts on one side of the conveyor run. Therefore, in a grain conveyor, the upper sprocket is normally driven.
The provision of additional idler sprockets in the linear elevator housing is not practical and so tensioning is typically done through longitudinal adjustment of one of the two sprockets around which the chain elevator is trained. In most grain conveyors, the upper sprocket lends itself better to adjustment than the lower sprocket because the latter has an associated transverse auger with critical clearances driven from the same shaft.
The linear adjustment of the driven sprocket brings with it some challenges, most notably the need to also maintain the desired tension in the belt or chain used to drive the conveyor. Therefore, the adjustment of the conveyor tension requires also an adjustment of the drive belt or pulley resulting in a rather cumbersome multistep process for the operator.
One approach to reduce the effect of adjusting the conveyor tension on the drive belt or chain tension would be to align the drive belt or chain perpendicular to the adjustment of the conveyor. However, this is rarely practical on a machine with limited available space.